Method and apparatus for detecting wobble defects in optical recording system

ABSTRACT

Aspects of the disclosure provide an apparatus. The apparatus includes a pick-up unit, such as an optical pick-up unit, a wobble channel and a defect detector. The pick-up unit generates a push-pull signal corresponding to a wobbled track of a storage medium. The wobble channel includes circuits to receive the push-pull signal, obtain a wobble signal from the push-pull signal, and calculate a wobble amplitude metric based on the wobble signal. The defect detector compares the wobble amplitude metric to a threshold to detect wobble defects.

INCORPORATION BY REFERENCE

This application claims the benefit of U.S. Provisional Application No.61/157,394, “Method and Apparatus for Detecting Wobble Defects inOptical Recording System” filed on Mar. 4, 2009, which is incorporatedherein by reference in its entirety.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Generally, a storage medium, such as an optical storage disc, wobbles arecording track to embed timing and address information. The timing andaddress information assists an optical recording device to record dataat appropriate locations of the wobbled recording track. For example,the optical recording device can include an optical pick-up unit coupledwith a wobble channel to extract the timing and address information. Theoptical pick-up unit generates a wobble signal corresponding to thewobbled recording track, and the wobble channel extracts the timing andaddress information from the wobble signal. Defects in the storagemedium can cause disturbances to the timing and address information, andcan cause loss of track to the timing and address information.

SUMMARY

Aspects of the disclosure can provide an apparatus. The apparatusincludes a pick-up unit, such as an optical pick-up unit, a wobblechannel and a defect detector. The pick-up unit generates a push-pullsignal corresponding to a wobbled track of a storage medium, such asfound on an optical disc. The wobble channel receives the push-pullsignal, obtains a wobble signal from the push-pull signal, andcalculates a wobble amplitude metric based on the wobble signal. Thedefect detector compares the wobble amplitude metric to a threshold todetect wobble defects.

In an embodiment, the wobble channel includes an envelope detector. Theenvelope detector detects a peak-to-peak envelope amplitude of thewobble signal. Then, the defect detector compares the peak-to-peakenvelope amplitude to the threshold to detect the wobble defects.

In another embodiment, the wobble channel further includes a wobbledemodulator to demodulate the wobble signal into an in-phase componentand a quadrature component. Then, the wobble amplitude metric iscalculated based on at least one of the in-phase component and thequadrature component. In an example, the wobble amplitude metric iscalculated based on only one of the in-phase component or the quadraturecomponent, such as an absolute value of the in-phase component, anabsolute value of the quadrature component, and the like. In anotherexample, the wobble amplitude metric is calculated based on a maximum ofthe in-phase component and the quadrature component, such as a maximumof absolute values of the in-phase component and the quadraturecomponent. In another example, the wobble amplitude metric is calculatedbased on a quadratic mean of the in-phase component and the quadraturecomponent, such as the quadratic mean, a square of the quadratic mean,and the like.

According to an aspect of the disclosure, the defect detector generatesa defect signal indicative of a wobble defect when the wobble amplitudemetric is smaller than the threshold. Further, at least one of thepick-up unit and the wobble channel is controlled based on the defectsignal.

Aspects of the disclosure can provide a method of detecting wobbledefects. The method includes generating a wobble signal in response to awobbled track of a storage medium, calculating a wobble amplitude metricbased on the wobble signal, comparing the wobble amplitude metric to athreshold, and detecting wobble defects based on the comparison.

Additionally, aspects of the disclosure can provide an integratedcircuit (IC). The IC includes a wobble channel and a defect detector.The wobble channel receives a push-pull signal, obtains a wobble signalfrom the push-pull signal, and calculates a wobble amplitude metricbased on the wobble signal. The defect detector compares the wobbleamplitude metric to a threshold to detect wobble defects.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of this disclosure that are proposed as exampleswill be described in detail with reference to the following figures,wherein like numerals reference like elements, and wherein:

FIG. 1 shows a block diagram of a medium apparatus example and anoptical disc example according to an embodiment of the disclosure;

FIG. 2 shows a block diagram of a wobble channel example coupled with anoptical pick-up unit example according to an embodiment of thedisclosure;

FIG. 3A shows a block diagram of a wobble demodulator example coupledwith a defect detector example according to an embodiment of thedisclosure;

FIG. 3B shows another block diagram of a wobble demodulator examplecoupled with a defect detector example according to an embodiment of thedisclosure;

FIG. 4 shows a block diagram of a timing loop filter example coupledwith a digital voltage control oscillator (DVCO) example according to anembodiment of the disclosure;

FIG. 5 shows a block diagram of a front-end portion in a wobble channelexample according to an embodiment of the disclosure; and

FIG. 6 shows a flow chart outlining a process example for detectingwobble defects according to an embodiment of the disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 shows a block diagram of a medium apparatus example 100 and astorage medium, such as an optical disc example 190 according to anembodiment of the disclosure. The medium apparatus 100 includes aprocessor 110, an optical drive 115, a random access memory (RAM) unit130, and a non-volatile memory 140. These elements can be coupledtogether as shown in FIG. 1.

The optical drive 115 includes various components, such as an opticalpick-up unit (OPU) 120, a wobble channel 125 having a defect detector,and the like. The OPU 120 generates various electrical signals, such aspush-pull signal, data signal, and the like, based on optical propertieson the optical disc 190. The wobble channel 125 includes suitablecircuits to obtain a wobble signal from the push-pull signal, andfurther obtain information embedded in the wobble signal. The embeddedinformation can assist the OPU 120 to record data on the optical disc190. Further, the defect detector of the wobble channel 125 detectswobble defects from the wobble signal, and generates a defect signalthat is indicative of the detected wobble defects. The defect signal canbe suitably used by the optical drive 115 to reduce disturbances due tothe wobble defects.

The optical disc 190 can be any suitable optical disc, such as CD,DVD-R, DVD-RW, DVD+R, DVD+RW, HD, Blu-Ray, and the like. Generally, theoptical disc 190 includes a spiral recording track, for example, in theform of a spiral groove adjacent to a spiral land. On the spiralrecording track, user data can be stored on a recording layer by formingeither data pits or data marks of different lengths and differentspacings. The length of a pit, or the space between two pits denotesdifferent information content or data information. To assist maintaininga uniform pit/mark length and pit/mark spacing, timing information andaddress information are embedded in the spiral groove and spiral landduring disc manufacturing. In an example, the timing information isembedded by wobbling the spiral groove and/or the spiral land. Further,the address information is embedded by various techniques, such as landpre-pits, wobble phase modulation, and the like. In addition, discinformation, such as manufacture, optical properties, and the like, isalso embedded in the spiral groove and/or the spiral land during discmanufacturing.

The OPU 120 can be suitably configured to generate electrical signals inresponse to the embedded information on the optical disc 190. In anembodiment, the OPU 120 includes servomechanisms (not shown) to direct alaser beam to a location of the optical disc 190. The laser beam isreflected from the location of the optical disc 190. The reflected laserbeam has light properties that correspond to information embedded at thelocation of the optical disc 190. The light properties are detected by alight detector (not shown) of the OPU 120. Further, the light detectorof the OPU 120 converts the light properties to various electricalsignals, such as a push-pull signal, and the like, for other componentsof the optical drive 115 to extract the embedded information.

In addition, the OPU 120 can be suitably configured to record user dataon the optical disc 190 based on the extracted embedded information,such as the timing information, the address information, the discinformation, and the like. In an embodiment, the servomechanisms of theOPU 120 are suitably controlled to direct a recording laser beam to arecording location of the optical disc 190. The recording location isdetermined based on the obtained address information. In addition, therecording laser beam is configured according to the obtained discinformation, and the turn-on time of the recording laser beam isdetermined based on the obtained timing information.

The wobble channel 125 obtains the wobble signal from the push-pullsignal, and detects wobbles in the wobble signal. Based on the detectedwobbles, the wobble channel 125 obtains various information to assistcontrols of the optical drive 115. More specifically, the wobble channel125 locks an internal clock to the wobble signal to obtain the embeddedtiming information in the wobbles. Further, the wobble channel 125extracts the embedded address information, the embedded discinformation, and the like, based on the locked wobble signal. Then, theextracted information is used by the optical drive 115 to control, forexample, the servomechanisms, the recording laser, and the like.

However, the wobble signal can be disturbed due to wobble defects on theoptical disc 190. The disturbances in the wobble signal can be detectedby the defect detector in the wobble channel 125. Thus, appropriateactions can be taken to mitigate the effects of the wobble defects. Forexample, when wobble defects are detected, the controls of theservomechanisms and the recording laser can be maintained according totheir previous statuses instead of being changed based on the wobblesignal.

In an example when wobble defects on the optical disc 190 are notdetected, the wobble defects disturb the wobble signal. The disturbancesin the wobble signal can cause the wobble channel 125 to inaccuratelydetect the wobbles, and lose locking of the internal clock to the wobblesignal. Thus, the timing information and the address information may beerroneously extracted, and the controls of the servomechanisms and therecording laser may be erroneously performed based on the disturbedwobble signal.

The processor 110 of the medium apparatus 100 executes system andapplication codes. The non-volatile memory 140 holds information evenwhen power is off. Thus, the non-volatile memory 140 can be used tostore system and application codes, such as firmware. The RAM unit 130is readable and writable. Generally, the RAM unit 130 has a fast accessspeed. In an example, data and the codes are stored in the RAM unit 130during operation, such that the processor 110 accesses the RAM unit 130for the codes and the data instead of the non-volatile memory 140.

It is noted that the medium apparatus 100 can include more than oneprocessor 110. In an example, the optical drive 115 includes a processorto execute software instructions for controlling the various componentsof the optical drive 115. It is also noted that the non-volatile memory140 can include various non-volatile memory devices, such as batterybackup RAM, read-only memory (ROM), programmable ROM (PROM), flash PROM,electrical erasable PROM (EEPROM), magnetic storage, optical storage,and the like. The RAM unit 130 can also include various RAM devices,such as DRAM, SRAM, and the like.

The medium apparatus 100 can include various other components. In anembodiment, the medium apparatus 100 includes a user input module 160.The user input module 160 enables a user to control operations of themedium apparatus 100. The user input module 160 includes various userinput devices, such as keyboard, mouse, touch screen, and the like. Inaddition, the user input module 160 includes interfaces for couplingexternal user input devices with the medium apparatus 100.

In another embodiment, the medium apparatus 100 includes an audio/video(A/V) module 150. The A/V module 150 includes various video and audiodevices, such as microphone, display screen, and the like. In addition,the A/V module 150 includes interfaces that couple external video andaudio devices with the medium apparatus 100. In an example, the opticaldisc 190 stores video data and audio data. The video devices and audiodevices play the video data and the audio data stored on the opticaldisc 190.

In another embodiment, the medium apparatus 100 includes communicationmodules, such as a network module 170, a wireless communication module180, and the like. The network module 170 and the wireless communicationmodule 180 enable the medium apparatus 100 to transmit the data storedon the optical disc 190 to other devices, or to store data received fromthe other devices onto the optical disc 190.

For ease and clarity of description, the embodiments are presented witha bus type architecture; however, it should be understood that any otherarchitectures can also be used to couple components within the mediumapparatus 100.

FIG. 2 shows a block diagram of a wobble channel example 225 coupledwith an optical pick-up unit (OPU) example 220 in an optical driveaccording to an embodiment of the disclosure. The wobble channel example225 is a more detailed example of the wobble channel 125 in FIG. 1, andthe OPU 220 is a more detailed example of the OPU 120 in FIG. 1. Thewobble channel 225 includes a front-end analog portion 230, a wobbledemodulator 240 and a defect detector 260. These elements are coupledtogether as shown in FIG. 2.

The OPU 220 includes a detector, such as a quadrant photo detector array210 shown in FIG. 2. The quadrant photo detector array 210 includes fourdetectors to detect a light beam 215, and generates various signals,such as a push-pull signal (PPS), based on the light beam 215. In theFIG. 2 example, the push-pull signal is generated according to Eq. 1:PPS=(I _(a) +I _(b))−(I _(c) +I _(d))  Eq. 1where I_(a), I_(b), I_(c) and I_(d) are current signals generated by thefour detectors in response to the light beam 215 reflected from awobbled recording track on a storage medium.

The front-end analog portion 230 receives the push-pull signal,regulates the push-pull signal, and outputs a wobble signal. Thefront-end analog portion 230 regulates the push-pull signal with analogtechniques for various purposes, such as amplification, compensation foroffsets, adjusting appropriate dynamic range, and the like. In anexample, the front-end analog portion 230 includes an offset loop thatadjusts the offsets of the push-pull signal. In another example, thefront-end analog portion 230 includes a gain loop that adjusts anamplifier gain to regulate the push-pull signal to an appropriatedynamic range. Thus, the outputted wobble signal is suitable forsubsequent circuit components to handle.

The wobble demodulator 240 receives the wobble signal, and extracts thetiming information from the wobble signal. More specifically, the wobbledemodulator 240 includes a phase-locked loop that locks an internalclock signal to the wobble signal to keep tracking timings embedded inthe wobbled recording track. Then, the internal clock signal is used bycomponents of an optical drive, such as the optical drive 115, toextract, for example, address information, disc information and thelike, embedded in the wobbled recording track. In addition, the internalclock signal is used to record user data with regard to the wobbledrecording track. Thus, the extraction and recording operations depend ona locking quality of the internal clock signal to the wobble signal.

Generally, the phase-locked loop locks the internal clock signal to thewobble signal based on a phase error. The phase error indicates a phasedifference of the internal clock signal and the wobble signal, forexample. The phase-locked loop pulls the phase error towards a stablepoint, such as zero. However, the phase error may shift from the stablepoint, due to various reasons, such as noises, disturbances,interferences, defects, and the like. The shifted phase error can resultin errors in the decoded information.

Wobble defects, such as scratches, block dots, and the like, can causelarge shifts in the phase error. In extreme cases, the wobble defectscan cause loss of timing lock of the internal clock signal to the wobblesignal. In an example, when the light beam 215 is reflected from adefective location on the wobbled recording track, the differencebetween the sum of I_(a) and I_(b), and the sum of I_(c) and I_(d) isreduced. Thus, the amplitude of the push-pull signal is reduced. In anextreme case, the push-pull signal does not correspond to the wobbledrecording track. In such case, the phase error can be substantiallyrandom. The random phase error can cause the phase-locked loop to loselocking of the internal clock signal to the wobble signal.

According to an aspect of the disclosure, the defect detector 260detects the wobble defects based on a wobble amplitude metric. Thewobble amplitude metric is calculated based on the wobble signal. In anembodiment, the wobble amplitude metric is provided to the defectdetector 260 by the front-end analog portion 230. Then, the defectdetector 260 detects wobble defects based on the wobble amplitude metricprovided by the front-end analog portion 230.

In another embodiment, the wobble amplitude metric is provided to thedefect detector 260 by the wobble demodulator 240. Then, the defectdetector 260 detects wobble defects based on the wobble amplitude metricprovided by the wobble demodulation 240.

The defect detector 260 outputs a defect signal corresponding to thewobble defect detection based on the wobble amplitude metric. In anexample, the defect detector 260 outputs logic one when the wobbleamplitude metric is smaller than a threshold and outputs logic zero whenthe wobble amplitude metric is larger than the threshold. In anembodiment, the defect signal is provided to a controller 270. Thecontroller 270 can control the operations of components in the opticaldrive, such as the OPU 220, the wobble channel 225, and the like, basedon the defect signal.

In an example, the controller 270 controls a servomechanism (not shown)within the OPU 220 based on the defect signal. More specifically, whenthe defect signal indicates no defect in the wobble signal, theservomechanism operates based on the wobble signal, for example, adjustsparameters based on the wobble signal. When the defect signal indicateswobble defects in the wobble signal, the servomechanism ignores thewobble signal for a time duration, or until the defect signal indicatesno defect in the wobble signal. The defect signal can be used by othercomponents, such as an offset loop, a gain loop, a timing loop, and thelike, to reduce disturbances due to the wobble defects.

In an embodiment, the front-end analog portion 230, the wobbledemodulator 240 and the defect detector 260 are implemented asintegrated circuit modules in one or more integrated circuit (IC) chips.The IC chips can further include other circuit modules, such ascontroller module, encoder module, decoder module, memory module,network module, and the like. The IC chips can be coupled with the OPU220 in an optical drive.

FIG. 3A shows a block diagram of a wobble demodulator 340 coupled with adefect detector example 360A according to an embodiment of thedisclosure. The wobble demodulator 340 is implemented as a timing loopincluding a quadrature demodulator 320, an analog-to-digital converter(ADC) 339, a timing loop filter 370, and a voltage control oscillator(VCO) 380. These elements are coupled together as shown in FIG. 3A.

The ADC 339 converts the wobble signal into a discrete wobble signalbased on a sampling clock signal from VCO 380. The quadraturedemodulator 320 computes a phase error signal between an internal clock(not shown) and the discrete wobble signal.

The timing loop filter 370 receives the phase error signal, and outputsa voltage signal based on the phase error signal. The voltage signal isreceived by the VCO 380 to generate the sampling clock signal.

The quadrature demodulator 320 demodulates the discrete wobble signalwith regard to the internal clock. More specifically, the quadraturedemodulator 320 includes two parallel signal processing paths togenerate a quadrature component and an in-phase component of thediscrete wobble signal with regard to the internal clock. The path togenerate the in-phase component includes a sine signal generator 343 ofthe internal clock, a multiplier 341 and an integrate and dump filter(I&D) 342. The path to generate the quadrature component includes acosine signal generator 346 of the internal clock, a multiplier 344 andan integrate and dump filter (I&D) 345. Subsequently, the quadrature andthe in-phase components are used by a phase and amplitude detector 350to generate the phase error as well as a wobble amplitude metric. Thewobble amplitude metric is used by the defect detector 360A to detectwobble defects.

During operation, for example, the sampling clock signal from the VCO380 samples the wobble signal to obtain the discrete wobble signal. Onthe in-phase path, the discrete wobble signal is multiplied with a sinesignal of the internal clock by the multiplier 341. Further, themultiplied signal is integrated over a period by the integrate and dumpfilter 342 to obtain the in-phase component.

On the quadrature path, the discrete wobble signal is multiplied with acosine signal of the internal clock by the multiplier 344. Further, themultiplied signal is integrated over a period by the integrate and dumpfilter 345 to obtain the quadrature component. Subsequently, thequadrature component and the in-phase component are used by the phaseand amplitude detector 350 to detect the phase error, for example usingan arctangent function. In addition, the phase and amplitude detector350 calculates a wobble amplitude metric based on the in-phase componentand the quadrature component. In an example, the phase and amplitudedetector 350 calculates a quadratic mean of the in-phase component andthe quadrature component, as shown by Eq. 2:Quadratic Mean=√{square root over (Q ² +I ²)}  Eq. 2where Q denotes the quadrature component, and I denotes the in-phasecomponent. Then, the wobble amplitude metric is calculated based on thequadratic mean. In an example, the wobble amplitude metric is thequadratic mean. In another example, the wobble amplitude metric is asquare of the quadratic mean.

Further, the timing loop filter 370 obtains a feedback portion based onthe phase error. The feedback portion is used by the VCO 380 to adjustthe sampling clock signal, such as its phase and frequency. Therefore,the sampling clock signal samples the wobble signal with a desiredfrequency and a desired phase. In an example, the wobble demodulator 340is configured to lock the internal clock to the wobble signal with zerophase error.

The internal clock is used by other components of an optical drive tocontrol operation timings. Therefore, the other components can operatecorresponding to the wobble signal as a result of the internal clockbeing locked to the wobble signal. However, due to wobble defects andother reasons, such as noises, and the like, the phase error of thewobble signal and the internal clock can be errantly shifted from, forexample, zero. The non-zero phase error can result in actions of thewobble demodulator 340 to erroneously attempt to lock the internal clockto the wobble signal having defect disturbances. The actions of thewobble demodulator 340 can cause the internal clock to lose locking tothe wobble signal.

The defect detector 360A declares a defect based on the wobble amplitudemetric provided by the phase and amplitude detector 350. In anembodiment, the defect detector 360A includes a comparator 361. Thecomparator 361 compares the wobble amplitude metric with a threshold todetect wobble defects. In an example, if the wobble amplitude metric issmaller than the threshold, the defect detector 360A detects a wobbledefect, and outputs logic one as the defect signal; otherwise, thedefect detector 360A outputs logic zero as the defect signal.

In an embodiment, the defect signal can be used by the timing loopfilter 370 to reduce disturbances due to the wobble defects. In anexample, the timing loop filter 370 is configured to disregard the phaseerror corresponding to the defect signal being logic one.

FIG. 3B shows another block diagram of the wobble demodulator 340coupled with a defect detector example 360B according to an embodimentof the disclosure. The defect detector 360B includes a multiplexer 362coupled with the comparator 361. The multiplexer 362 receives thein-phase component from the integrate and dump filter 342, thequadrature component from the integrate and dump filter 345, and acombination of the in-phase component and the quadrature component, suchas a quadratic mean of the in-phase component and the quadraturecomponent, a maximum of the in-phase component and the quadraturecomponent, and the like, provided by the phase and amplitude detector350. The multiplexer 362 can be suitably controlled to select one of thein-phase component, the quadrature component, and the combination of thein-phase component and the quadrature component, and provide theselected to the comparator 361. Then, the comparator 361 compares theselected to a suitable threshold, and generates the defect signal basedon the comparison.

It is noted that suitable operations can be conducted on the in-phasecomponent and/or the quadrature component. In an example, positivevalues are used in the defect detector 360B to detect defects. Thus,absolute values of the in-phase components and the quadrature componentare calculated and provided to the multiplexer 262. Further, theabsolute values are used to determine the maximum of the in-phasecomponent and the quadrature component.

It is noted that the multiplexer 362 can be removed, and the comparator361 is suitably coupled to the integrated and dump filter 342, theintegrated and dump filter 345 and/or the phase and amplitude detector350. In an example, the comparator 361 is coupled to the integrate anddump filter 342 to receive the in-phase component, and the comparator361 generates the defect signal based on comparing the in-phasecomponent to a suitable threshold. In another example, the comparator361 is coupled to the integrate and dump filter 345 to receive thequadrature component, and the comparator 361 generates the defect signalbased on comparing the quadrature component to a suitable threshold. Inanother example, the comparator 361 is coupled to the phase andamplitude detector 350 to receive a maximum of the in-phase componentand the quadrature component, and the comparator 361 generates thedefect signal based on comparing the maximum of the in-phase componentand the quadrature component to a suitable threshold. In anotherexample, the comparator 361 is coupled to both the integrate and dumpfilter 342 and the integrate and dump filter 345 to receive both thein-phase component and the quadrature component. The comparator 361 caninclude any suitable comparison algorithm, or any suitable comparisonlogic to generate the defect signal based on comparing the in-phasecomponent and/or the quadrature component, or functions of the in-phaseand/or quadrature components to suitable thresholds.

FIG. 4 shows a block diagram of a timing loop filter example 470 coupledwith a digital voltage control oscillator (DVCO) example 480 accordingto an embodiment of the disclosure. The timing loop filter 470 includesa phase path and a frequency path to generate a control signal for theDVCO 480. The phase path includes a first multiplier 472 to generate aphase component. The frequency path includes a second multiplier 474 andan integrator 475 to generate the frequency component. The integrator475 includes a first adder 476 and a register 478. Further, the timingloop filter 470 includes a second adder 479 to combine the phasecomponent and the frequency component to generate the control signal.These elements are coupled together as shown in FIG. 4.

The first multiplier 472 multiplies the phase error with a phase updategain to generate the phase component. The phase update gain can betunable. For example, the phase update gain can be tuned to one of 16values. In an example, when wobble defects are detected, for example, asindicated by the defect signal being logic one, the phase update gain istuned to a suitable value, such as zero, to disregard the phase error.

The second multiplier 474 multiplies the phase error with a frequencyupdate gain. Then, the integrator 475 integrates the multiplied phaseerror to generate the frequency component. More specifically, the firstadder 476 adds the multiplied phase error to a previous frequencycomponent to generate a current frequency component. The register 478holds the previous frequency component. The previous frequencycomponents is then used to generate the current frequency component. Thefrequency update gain can be tunable. For example, the frequency updategain can be tuned to one of 16 values. In an example, when wobbledefects are detected, for example, as indicted by a defect signal beinglogic one, the frequency update gain is tuned to a suitable value, suchas zero, to disregard the phase error.

Further, the second adder 479 combines the phase component and thefrequency component to generate the control signal for the DVCO 480. Inan embodiment, the DVCO 480 includes a digital representation of avoltage signal. The control signal is used to adjust the digitalrepresentation of the voltage signal. The DVCO 480 further includes adigital to analog converter (DAC) (not shown). The DAC converts thedigital representation to the voltage signal. Further, the voltagesignal is used to control a voltage control oscillator (VCO) to generatethe sampling clock accordingly.

FIG. 5 shows a block diagram of a front-end portion example 530 coupledto a defect detector 560 according to an embodiment of the disclosure.The front-end portion 530 includes an offset adder 531, a variable gainamplifier (VGA) 532, a continuous time filter (CTF) 533, an analog todigital converter (ADC) 539, an envelope detector 536, a gain loopcontroller 534, and an offset loop controller 535. These elements arecoupled together as shown in FIG. 5.

The offset adder 531, the VGA 532, and the CTF 533 regulate a receivedanalog signal to have desired properties. For example, the offset adder531 adjusts the analog signal with an offset provided by the offset loopcontroller 535. The VGA 532 amplifies the analog signal with a gaincontrolled by the gain loop controller 534. The CTF 533 truncates anoise bandwidth of the analog signal, for example.

The ADC 539 obtains a discrete wobble signal by sampling the regulatedanalog signal. The envelope detector 536 detects envelopes of thediscrete wobble signal. Then, the offset loop controller 535 generatesthe offset based on the envelopes, and the gain loop controller 534generates the gain based on the envelopes. Also, the defect detector 560detects wobble defects based on the envelopes. In an embodiment, thedefect detector 560 detects the wobble defects based on a peak-to-peakenvelope amplitude. In an example, the defect detector 560 includes acomparator 561. The comparator 561 compares the peak-to-peak envelopeamplitude to a threshold to generate a defect signal. For example, whenthe peak-to-peak envelope amplitude is smaller than the threshold, thecomparator 561 outputs logic one as a defect signal to indicate a wobbledefect; otherwise, the comparator 561 outputs logic zero.

It is noted that the envelope detector 536 and the front-end portion 530can be suitably adjusted to detect wobble signal envelopes before thewobble signal is sampled by the ADC 539.

FIG. 6 shows a flow chart outlining a process example 600 for an opticaldrive to detect wobble defects according to an embodiment of thedisclosure. The process 600 starts at S610, and proceeds to S620.

At S620, the optical drive generates a wobble signal in response to awobbled recording track. In an example, the optical drive includes anOPU, such as the OPU 220, and a wobble channel, such as the wobblechannel 225. The OPU directs a laser beam onto the wobbled recordingtrack, and detects a reflected laser beam. The OPU generates a push-pullsignal in response to the reflected laser beam. The wobble channel 225regulates the push-pull signal to generate the wobble signal.

At S630, the optical drive calculates a wobble amplitude metric. In anembodiment, the wobble channel 225 includes an envelope detector todetect a peak-to-peak envelope amplitude of the wobble signal. Inanother embodiment, the wobble channel 225 includes a wobbledemodulator. The wobble demodulator demodulates the wobble signal withregard to an internal clock to generate an in-phase component and aquadrature component. The in-phase component and the quadraturecomponent can be used to calculate a phase error of the wobble signal tothe internal clock. In addition, at least of the in-phase component andthe quadrature component can be used to calculate the wobble amplitudemetric. In an example, the wobble amplitude metric is calculated basedon only the in-phase component. For example, the wobble amplitude metricis calculated as an absolute value of the in-phase component, or ascaled in-phase component. In another example, the wobble amplitudemetric is calculated based on a maximum of the in-phase component andthe quadrature component. For example, the wobble amplitude metric iscalculated as a maximum of absolute values of the in-phase component andthe quadrature component. In another example, the wobble amplitudemetric is calculated based on a quadratic mean of the in-phase componentand the quadrature component. For example, the wobble amplitude metricis calculated as the quadratic mean or a square of the quadratic mean.

At S640, the optical drive compares the wobble amplitude metric to athreshold. In an example, the optical drive compares the peak-to-peakenvelope amplitude to a threshold. In another example, the optical drivecompares an absolute value of the in-phase component to a threshold. Inanother example, the optical drive compares the maximum of the absolutevalue of the in-phase component and the absolute value of the quadraturecomponent to a threshold. In another example, the optical drive comparesthe quadratic mean of the in-phase component and the quadraturecomponent to a threshold.

At S650, the optical drive detects wobble defects based on thecomparison. In an example, when the wobble amplitude metric is smallerthan the threshold, the optical drive outputs a defect signal indicativeof a wobble detect, such as the defect signal being logic one.Otherwise, the optical drive outputs logic zero as the defect signal,for example. The defect signal can be used by the optical drive toadjust various components to reduce disturbances due to the wobbledefects. Then, the process proceeds to S660 and terminates.

It is noted that the process 600 can be continuously performed by theoptical drive during a recording process. It is also noted that thethreshold can be static or dynamic, and can be suitably calibrated fordifferent wobble amplitude metrics.

While the invention has been described in conjunction with the specificembodiments thereof that are proposed as examples, it is evident thatmany alternatives, modifications, and variations will be apparent tothose skilled in the art. Accordingly, embodiments of the invention asset forth herein are intended to be illustrative, not limiting. Thereare changes that may be made without departing from the scope of theinvention.

1. An apparatus, comprising: a pick-up unit configured to generate apush-pull signal corresponding to a wobbled track of a storage medium; awobble channel configured to receive the push-pull signal, obtain awobble signal from the push-pull signal, and calculate a wobbleamplitude metric based on the wobble signal, wherein the wobble channelincludes a wobble demodulator configured to demodulate the wobble signalinto at least one of an in-phase component and a quadrature component,the wobble amplitude metric being calculated based on the at least oneof the in-phase component and the quadrature component; and a defectdetector configured to compare the wobble amplitude metric to athreshold to detect wobble defects.
 2. The apparatus of claim 1, whereinthe wobble amplitude metric is calculated based on only one of thein-phase component or the quadrature component.
 3. The apparatus ofclaim 1, wherein the wobble amplitude metric is calculated based on atleast one of a maximum of absolute values of the in-phase component andthe quadrature component, and a quadratic mean of the in-phase componentand the quadrature component.
 4. The apparatus of claim 1, wherein thepick-up unit is an optical pick-up unit.
 5. The apparatus of claim 1,wherein the defect detector is configured to generate a defect signalindicative of a wobble defect when the wobble amplitude metric issmaller than the threshold.
 6. The apparatus of claim 5, wherein atleast one of the pick-up unit and the wobble channel is controlled basedon the defect signal.
 7. A method of detecting wobble defects,comprising: generating a wobble signal in response to a wobbled track ofa storage medium; demodulating the wobble signal to generate at leastone of component and a quadrature component; calculating a wobbleamplitude metric based on the at least one of the in-phase component andthe quadrature component; comparing the wobble amplitude metric to athreshold; and detecting wobble defects based on the comparison.
 8. Themethod of claim 7, wherein the wobble amplitude metric is calculatedbased on only one of the in-phase component or the quadrature component.9. The method of claim 7, wherein the wobble amplitude metric iscalculated based on at least one of a maximum of absolute values of thein-phase component and the quadrature component, and a quadratic mean ofthe in-phase component and the quadrature component.
 10. The method ofclaim 7, wherein generating the wobble signal in response to the wobbledtrack of the storage medium further comprises: converting a light signalreflected from the wobble track to the wobble signal.
 11. An integratedcircuit (IC), comprising: a wobble channel configured to receive apush-pull signal, obtain a wobble signal from the push-pull signal, andcalculate a wobble amplitude metric based on the wobble signal, whereinthe wobble channel includes a wobble demodulator configured todemodulate the wobble signal to generate at least one of an in-phasecomponent and a quadrature component, the wobble amplitude metric beingcalculated based on the at least one of the in-phase component and thequadrature component; and a defect detector configured to compare thewobble amplitude metric to a threshold to detect wobble defects.
 12. TheIC of claim 11, wherein the wobble amplitude metric is calculated basedon only one of the in-phase component or the quadrature component. 13.The IC of claim 11, wherein the wobble amplitude metric is calculatedbased on at least one of a maximum of absolute values of the in-phasecomponent and the quadrature component, and a quadratic mean of thein-phase component and the quadrature component.
 14. The IC of claim 11,wherein the defect detector is configured to generate a defect signalindicative of a wobble defect when the wobble amplitude metric issmaller than the threshold.
 15. An apparatus, comprising: integratedcircuit, the integrated circuit including: a wobble channel configuredto receive a push-pull signal, obtain a wobble signal from the push-pullsignal, wherein the wobble channel includes an envelope detectorconfigured to calculate a peak-to-peak envelope amplitude of the wobblesignal; and a defect detector configured to compare the peak-to-peakenvelope amplitude of the wobble signal to a threshold to detect wobbledefects.
 16. The apparatus of claim 15, further comprising: an opticalpick-up unit configured to generate the push-pull signal correspondingto a wobbled track of a storage medium.
 17. The apparatus of claim 15,wherein the defect detector is configured to generate a defect signalindicative of a wobble defect when the peak-to-peak envelope amplitudeis smaller than the threshold.
 18. The apparatus of claim 17, wherein atleast one of the optical pick-up unit and the wobble channel iscontrolled based on the defect signal.
 19. A method of detecting wobbledefects, comprising: receiving a wobble signal in response to a wobbledtrack of a storage medium; calculating a peak-to-peak envelope amplitudeof the wobble signal; comparing the peak-to-peak envelope amplitude to athreshold; and detecting a wobble defect based on the comparison. 20.The method of claim 19, wherein detecting the wobble defect based on thecomparison further comprises: detecting the wobble defect when thepeak-to-peak envelope amplitude is smaller than the threshold.